1. Field of the Invention
The present invention relates to a sheet conveying apparatus; an image scanning apparatus such as a copier, a facsimile machine, a printer, a printing machine, an inkjet recording device, and a scanner provided with the sheet conveying apparatus; or an image forming apparatus such as a multifunction peripheral combining functions of at least two of the above.
2. Description of the Related Art
Conventionally, in order to reduce the overall sizes of image forming apparatuses including copiers such as a PPC (plain paper copier) and an electrophotographic copier, facsimile machines, printers such as a laser beam printer, printing machines, and inkjet recording devices, the sizes of conveying units provided therein also tend to be reduced. Specifically, the conveying unit is used for conveying a medium or a sheet-type recording medium onto which an image is formed (hereinafter, “sheet”). The sheet is conveyed from a sheet storing unit or a sheet stacking unit where sheets are stacked to a main unit of an image forming unit (hereinafter, “image forming unit main unit”). In the following, the sheet storing unit is described as a representative example of a unit for storing sheets.
Furthermore, the image forming apparatuses typically accommodate various sheet sizes and sheet types. For example, sheets of different sheet sizes and different sheet types are previously stored in plural sheet storing units. A sheet is fed from the sheet storing unit selected by a user or automatically selected by the image forming apparatus. In such a configuration, the sheet storing units occupy a large space in the image forming apparatus, and therefore, it is particularly necessary to reduce the size of the conveying unit.
One approach is to have a conveying path between the sheet storing unit and the image forming unit main unit that considerably changes its direction midway (bends) depending on the positional relationship between the two units, so as to reduce the space occupied by the conveying path. Thus, in order to change the conveying direction in a continuous and smooth manner in the conveying path, the conveying path is provided with a curvature section having a curved shape. The curvature section is made to have a relatively small curvature radius so that a regular-sized recording sheet normally used in the image forming apparatus can be conveyed.
An example of a conventional sheet conveying apparatus in an image forming apparatus is disclosed in Japanese Laid-Open Patent Application No. 2004-338923 (Patent Document 1). As shown in FIGS. 6, 7 of Patent Document 1, sheet feeding trays acting as sheet storing units are arranged beneath the image forming unit main unit. Predetermined numbers of sheets of predetermined sheet sizes and sheet types are stacked in the sheet feeding trays. In between the sheet feeding trays and the image forming unit main unit is provided a sheet conveying apparatus for extracting a sheet of paper in a substantially horizontal direction from the selected sheet feeding tray and feeding the extracted sheet in an upward direction toward the image forming unit main unit arranged above.
In the following description, reference numerals shown in the figures of Japanese Laid-Open Patent Application No. 2004-338923 are indicated in parentheses. A sheet (P) in a sheet feeding tray (1) is separated from the stack of sheets by the conventional FRR (Feed Reverse Roller) separating method, and is sent to an image forming unit main unit through a conveying path provided with a curvature section formed with an upper guide plate (8) and a lower guide plate (7). The curvature section acts as a “curve fix guiding member” including the upper guide plate (8) and the lower guide plate (7). When the sheet passes through the curvature section, the sheet is first conveyed along the lower guide plate (7). As the sheet is conveyed further on, the sheet is pressed from above by the upper guide plate (8). The sheet (P) is conveyed by an elastically deformable guide piece (6) positioned at the outlet end of the lower guide plate (7) and reaches a pair of conveying rollers (5). Hereinafter, the upper guide plate (8) and the lower guide plate (7) are referred to as the “curve fix guiding member”.
However, in the sheet conveying apparatus with the above configuration, the following problem arises when conveying a special type of sheet (P) with high rigidity, such as a cardboard recording paper or an envelope. That is, when the sheet (P) bends and moves along the curvature, such a highly rigid recording paper or special paper receives a much larger resistance compared to a regular sheet such as a plain paper sheet used for copying. This is because the curvature section in the conveying path has a small radius. As a result, the highly rigid sheet (P) cannot move along the conveying path, causing a paper jam failure or a conveyance failure. Thus, the sheet feeding operation cannot be steadily performed.
Further details of the above operation are described as follows. When the leading edge of the sheet (P) in the sheet conveying direction reaches the curve fix guiding member configured with the upper guide plate (8) and the lower guide plate (7), the front half the sheet (P) including the leading edge curves (bends) in its thickness direction. Accordingly, when a highly rigid sheet (P) is conveyed, a large force resists this bending action, in such a manner that a large resistance obstructs the sheet conveyance. As a result, the leading edge of the highly rigid sheet (P) may not reach the pair of conveying rollers (5) at the downstream side so that the sheet (P) is conveyed only by a pair of rollers (2a, 2b) on the upstream side. However, when the sheet (P) is bent by the curve fix guiding member, the conveying force of the pair of rollers (2a, 2b) alone is insufficient for conveying the highly rigid sheet (P) to counter to the resistance caused by the bending action. As a result, the following conveyance failures may be caused. Specifically, the sheet (P) is caused to move in an oblique manner because the center line of the highly rigid sheet (P) does not match the center line of the conveying path, or a paper jam occurs because the highly rigid sheet (P) becomes caught inside the curve fix guiding member and stops moving.
Accordingly, Japanese Laid-Open Patent Application No. 2004-338923 also discloses the following sheet feeding device. A sheet is sent out from a first conveying member and conveyed to a second conveying member arranged at a position downstream in the conveying direction and substantially perpendicularly above the first conveying member. A pair of linear guiding members is provided between the first conveying member and the second conveying member, and the sheet is conveyed by being guided by these linear guiding members. In this sheet feeding device, the guiding members do not have curved shapes but have linear shapes, and therefore, the conveyance load can be maintained at a low level. That is, the load can be prevented from rising abruptly so that conveyance failures such as a paper jam or oblique movements can be prevented.
That is, according to the above described sheet feeding device, the conveyed sheet is not caused to deform (bend) only at one position, but is caused to deform at two positions, i.e., near the front and the back ends of the linear guiding members in the conveying direction. Furthermore, the linear guiding members are arranged in oblique manners at substantially intermediate angles, so that the sheet bends by the same amount at the aforementioned two positions. Therefore, the conveyance load is prevented from rising abruptly. Specifically, the sheet changes its traveling direction by bending at the two positions, namely, when the sheet is passed from the pair of rollers located at the upstream side to the linear guiding member, and when the sheet is passed from the linear guiding member to the pair of rollers located at the downstream side. Thus, the sheet bends by smaller extents at these two positions compared to abruptly bending at one position. Thus, the resistance caused by the bending action of the sheet can be reduced at each of the two positions, thus preventing the conveyance load from rising abruptly.
Another type of sheet feeding device with a first conveying member and a second conveying member having substantially the same configurations as those of Japanese Laid-Open Patent Application No. 2004-338923 (Patent Document 1) is described as follows. This type includes a reverse guiding member provided in an inclined manner between the first conveying member and the second conveying member. This reverse guiding member is configured to move toward the second conveying member (see, for example, Patent Document 2).
In this sheet feeding device, when the trailing edge of the sheet contacts the reverse guiding member, the reverse guiding member shifts its position in a direction substantially according to the trailing edge of the sheet. This shift makes it possible to absorb the shock caused when the trailing edge of the sheet contacts the reverse guiding member. Hence, a flipping noise can be reduced.
Yet another type of sheet feeding device has been disclosed. This sheet feeding device includes plural sheet storing units for storing sheets, and each of the sheet storing units is provided with a conveying path and a sheet conveying unit. The ends of the conveying paths merge into a common conveying path. Each of the conveying paths has a curvature section at the end thereof where it merges with the common conveying path. At least one of the conveying paths provided for a sheet storing unit storing highly rigid sheets has a first curvature section with a larger curvature radius than those of the other conveying paths (see, for example, Patent Document 3).
Therefore, in this sheet feeding device, highly rigid sheets are caused to bend more moderately compared to plain paper sheets. A highly rigid sheet moves along the conveying path and passes through the first curvature section having a large curvature radius, so that it does not bend as much as a plain paper sheet passing through a curvature section having a smaller curvature radius. Accordingly, it is possible to reduce the resistance while conveying a highly rigid sheet, so that the sheet is conveyed to the common conveying path without being suspended or stopped.
The following is a description of a sheet reversing unit provided in an image forming apparatus. This sheet reversing unit includes a pair of reverse rollers and a reverse conveying path for conveying/guiding a sheet received from the pair of reverse rollers. The reverse conveying path includes a direction changing section for changing the direction of conveying a sheet. Rotatable rollers are arranged inside the direction changing section in a direction orthogonal to the sheet conveying direction, so that a sheet sent into the reverse conveying path can be sent out while being in abutment with the rollers (see, for example, Patent Document 4).
According to this sheet reversing unit, when a sheet is sent inside, it is ensured that the portion of the sheet inside of the direction changing section contacts the rollers, and the rollers are caused to rotate by (rotate following) the movement of the sheet in the conveying direction. Thus, compared to a conventional guiding plate, the conveying resistance can be reduced. Specifically, it is possible to eliminate frictional resistance occurring between a fixed guiding member and the moving sheet while changing the conveying direction of the sheet at the direction changing section.    Patent Document 1: Japanese Laid-Open Patent Application No. 2004-338923 (pp. 1-3, FIGS. 1-7)    Patent Document 2: Japanese Laid-Open Patent Application No. 2005-89008 (pp. 2-3, FIGS. 4, 5)    Patent Document 3: Japanese Laid-Open Patent Application No. H10-129883 (pp. 1-2, FIG. 1)    Patent Document 4: Japanese Laid-Open Patent Application No. 2005-1771 (pp. 1-2, FIG. 1)
However, the sheet conveying apparatus disclosed in Patent Document 1 merely provides a fixed member for guiding a conveyed sheet, and thus does not eliminate the speed difference between the conveyed sheet, which is a mobile object, and the fixed guiding member. Accordingly, regardless of the shape or position of the guiding member, resistance occurs in such a direction to obstruct the sheet from being conveyed, resulting in a conveyance load.
That is, this conventional configuration is insufficient for preventing conveyance failures or paper jams. Although the linear guiding member can reduce the conveyance load from rising abruptly, a conveyance load is generated nonetheless. Particularly when conveying a highly rigid sheet, such as a cardboard recording paper or an envelope, conveyance failures and paper jams frequently occur and flipping noises made by the trailing edge of the sheet become considerably large.
Furthermore, as described in Patent Document 2, the reverse guiding member can shift its position in a direction according to the trailing edge of the sheet contacting the reverse guiding member; however, the reverse guiding member merely functions as a fixed guide member in terms of changing the direction of the sheet. Accordingly, similar to the above, this conventional technology does not eliminate the relative speed difference between the sheet and the reverse guiding member when changing the direction of/guiding the sheet, thus generating a conveyance load. Particularly when conveying a highly rigid sheet, such as a cardboard recording paper or an envelope, conveyance failures and paper jams frequently occur and flipping noises made by the trailing edge of the sheet become considerably large.
Furthermore, as described in Patent Document 3, the conveying path with a large curvature radius dedicated for highly rigid sheets makes it possible for sheets traveling therethrough to bend moderately so as to reduce the conveyance resistance applied from the conveying path on the sheet. However, a conveyance load is somewhat generated nonetheless. Particularly when conveying a highly rigid sheet, such as a cardboard recording paper or an envelope, conveyance failures and paper jams frequently occur.
Furthermore, as described in Patent Document 4, movable members such as rollers are provided at predetermined positions inside the direction changing section of the conveying path. Therefore, in the process of conveying the sheet, the frictional resistance between the sheet and the guiding member can be effectively reduced while the internal rollers are supporting the middle portion of the sheet between the leading edge and the trailing edge. However, there are no measures provided for reducing the conveyance load before and after the sheet is supported by the internal rollers, i.e., when the sheet is in contact with the conveying path outside the direction changing section. Furthermore, nothing is particularly mentioned about behaviors of the leading edge and the trailing edge of the sheet while being conveyed. Particularly when conveying a highly rigid sheet, such as a cardboard recording paper or an envelope, conveyance failures and paper jams frequently occur and flipping noises made by the trailing edge of the sheet become considerably large.